Guidewire with imaging capability

ABSTRACT

A guidewire imaging catheter includes a catheter body, housing secured to the distal end of the catheter body, a drive cable extending through a central lumen of the catheter body, and an imaging system disposed within the housing and coupled to the drive cable. A fixed guidewire is secured to the distal tip of the housing, and the catheter body is highly flexible while retaining sufficient torsional stiffness to allow the entire catheter to be used as a guidewire. Thus, the imaging guidewire can be used to first image a desired region within a patient&#39;s vascular system and subsequently as a guidewire to allow placement of a desired interventional catheter.

This is a Continuation of application Ser. No. 08/320,105, filed Oct. 5,1994, now abandoned which was a CIP of U.S. Ser. No. 08/113,972(Abandoned), which was a CIP of U.S. Ser. No. 07/846,304; filed Mar. 5,1992 (Abandoned), which was a CIP of U.S. Ser. No. 07/525,948; filed May18, 1990 now U.S. Pat. No. 5,095,911.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the construction and use ofvascular catheters and, more particularly, to catheters which may beused both as a guidewire for positioning larger catheters and as anultrasonic imaging catheter.

Arteriosclerosis, also known as atherosclerosis, is a common humanailment arising from the deposition of fatty-like substances, referredto as atheroma or plaque, on the walls of blood vessels. Such depositsoccur both in peripheral blood vessels that feed the limbs of the bodyand coronary blood vessel which feed the heart. When deposits accumulatein localized regions of a blood vessel, blood flow is restricted and theperson's health is at serious risk.

Numerous approaches for reducing and removing such vascular depositshave been proposed, including balloon angioplasty, where aballoon-tipped catheter is used to dilatate a region of atheroma;atherectomy, where a blade or other cutting element is used to sever andremove the atheroma; and laser angioplasty, where laser energy is usedto ablate at least a portion of the atheroma. In addition to suchtherapeutic approaches, a variety of techniques for transluminal imagingof atheroma and other diseased regions of a blood vessel has beenproposed, including endoscopic imaging techniques and ultrasonic imagingtechniques. Common to all such techniques is the use of an intravascularcatheter which is positioned at a desired location within the bloodvessel to be treated or imaged.

Two alternative approaches may generally be employed to achieve suchpositioning. In the first approach, the vascular catheter is providedwith a "fixed guidewire" secured to its distal end. The fixed guidewireis typically a coiled spring or other elongate resilient member having apreformed, curved tip. The catheter can then be guided through brancheswithin the vascular network by rotating the entire catheter, causing thetip of the guidewire to enter a desired branch as the catheter is movedforward. In the second technique, an entirely separate "movableguidewire" is employed. The movable guidewire is itself a coiled springor other resilient elongate member and will generally include a curvedtip similar to that provided on the fixed guidewires described above.The vascular catheter being positioned includes a guidewire lumen whichgenerally extends down the center of the entire length of the catheterand is sized to receive the movable guidewire. The movable guidewire isfirst positioned within the vascular system so that its distal endextends beyond the region of interest, and the intravascular catheter isthen inserted over the movable guidewire using the guidewire lumen. Suchprocedures using movable guidewires are commonly referred to as"over-the-wire" insertional techniques.

Recently, ultrasonic imaging catheters have been developed for use inconjunction with various interventional therapies, includingangioplasty, atherectomy, laser ablation, and the like. By imaging adiseased region prior to therapy, the treatment can be more preciselydirected to both enhance effectiveness and reduce deleterious sideeffects. Such ultrasonic imaging catheters have generally beenintroduced prior to therapy, typically using a movable guidewire as justdescribed or a fixed-tip guidewire which is secured to the forward endof the imaging catheter. After imaging has been completed, it hasgenerally been necessary to remove the imaging catheter prior totherapy, although in some cases it has been proposed to provide aparticular interventional capability on the imaging catheter itself.

The need to remove the imaging catheter before employing conventionalinterventional catheters is time consuming and increases the risk thatthe blood vessel wall will be damaged or that emboli will beaccidentally dislodged. Moreover, once removed, the imaging catheter isno longer available for imaging during the therapeutic procedure unlessanother time-consuming catheter-exchange procedure is employed.

For these reasons, it would be desirable to provide ultrasonic imagingcatheters which may also serve as a guidewire for the introduction oflarger interventional catheters. Preferably, such imaging guidewirecatheters should employ a rotating ultrasonic imaging system where anultrasonic transducer, a reflective surface, or both, are rotated inorder to sweep a continuous ultrasonic signal about the interior of theblood vessel wall.

2. Description of the Background Art

PCT application WO 89/07419 discloses a miniature ultrasonic imagingprobe where an ultrasonic transducer is attached to the distal end of acoaxial cable within a holder. The transducer and an acoustic reflectorare rigidly maintained within the holder. The ultrasonic transducercannot be moved within the probe, and it would be necessary to rotatethe entire transducer in order to image an annular section of a bloodvessel. Such rotation would be deleterious to the blood vessel wall.Probes of the type described in WO 89/07419 are employed inside aprotective sheath that remains stationary and covers the entire probeduring imaging procedures where the probe is rotated. U.S. Pat. No.4,794,931, describes an ultrasonic imaging catheter where a rotatingtransducer, or a rotating mirror in combination with a fixed transducer,is mounted within a housing at the distal end of the catheter. Guidewirecatheters are described in various patents, including U.S. Pat. Nos.4,747,406; 4,724,846; 4,682,607; and 3,416,531. Copending applicationSer. No. 07/500,818 filed Mar. 28, 1990 and now U.S. Pat. No. 5,108,411,the disclosure of which is incorporated herein by reference, describesdrive cables suitable for use with catheters having rotating distal workelements, where the flexibility of the cable is increased near itsdistal end.

SUMMARY OF THE INVENTION

A catheter is provided which is capable of both ultrasonic imaging andintroducing larger catheters for interventional treatment, such asangioplasty, atherectomy, laser ablation, and the like. The catheter ofthe present invention comprises a very flexible catheter body having avery small diameter, typically from about 0.3 mm to 1 mm. The bendingstiffness constant of the catheter body is very low, typically being inthe range from about 1 in-lb-in to 15 in-lb-in, while the torsionalstiffness constant is relatively high, typically being in the range fromabout 0.5 in-lb-in/radian to 7 in-lb-in/radian, so that the distal tipof the catheter can be rotated to facilitate initial positioning withina patient's vascular system. A housing is attached to the distal end ofthe catheter body, and a drive cable extends through a central lumen inthe catheter body from a distal end to a proximal end. To providehigh-quality images, a rotating ultrasonic imaging system is disposedwithin the housing and coupled to the drive. Preferably, the imagingsystem includes an ultrasonic transducer and a reflective surface whichare fixedly interconnected to rotate together as the drive cable isrotated. The reflective surface is disposed to project an ultrasonicsignal in a generally transverse direction relative to the housing. In afirst alternate embodiment, the ultrasonic transducer is attacheddirectly to the drive cable and disposed to direct the ultrasonic signalin the transverse direction without the need of a reflective surface. Ina second alternative embodiment, the transducer is fixedly mountedwithin the housing, and only a reflective surface is attached to thedrive cable. Such a rotating reflective surface can sweep the ultrasonicsignal from the transducer in the desired transverse pattern about theblood vessel wall.

In the method of the present invention, the guidewire imaging catheteris first positioned within the patient's vascular system in a mannersimilar to that employed with conventional guidewires. After initialpositioning, the imaging system of the guidewire is used to obtaininitial images of the untreated, diseased region within the bloodvessel. It is an advantage of the present invention that the image canbe obtained without the need to rotate the entire catheter or place thecatheter within a protective sheath, as is the case with the catheterdescribed in PCT application WO 89/07419, discussed above. After thefirst image is obtained, a treatment regimen can be planned and aninterventional catheter introduced with the imaging guidewire used as aconventional guidewire. Treatment is performed on the diseased region,again in a conventional manner. During treatment, however, it ispossible to periodically produce images of the blood vessel wall toobtain feedback on how the therapy is proceeding. These images can beobtained without the need to remove the interventional catheter,although it will frequently be desirable to move the interventionalcatheter a short distance away from the region being treated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the distal end of a preferredguidewire imaging catheter constructed in accordance with the principlesof the present invention.

FIG. 2 is a cross-sectional view of the distal end of a first alternateembodiment of a guidewire imaging catheter constructed in accordancewith the principles of the present invention.

FIG. 3 is a cross-sectional view of the distal end of a second alternateembodiment of a guidewire imaging catheter constructed in accordancewith the principles of the present invention.

FIGS. 4-7 illustrate the method of the present invention where theguidewire imaging catheter is used to position an angioplasty ballooncatheter within a stenosed region in a blood vessel for treatment.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Catheters constructed in accordance with the principles of the presentinvention will comprise an elongate flexible catheter body having aproximal end, a distal end, and a central lumen extending therebetween.The catheter body comprises a highly flexible structure capable ofinsertion into and manipulation within a patient's vascular system. Thedimensions of the catheter body will depend on use, with the lengthvarying widely, typically being between about 100 cm and 200 cm, usuallybeing between about 125 cm and 175 cm. The catheter body diameter willvary less widely, typically being below about 1 mm in diameter, usuallybeing between about 0.3 mm and 1 mm in diameter, and more usually beingbetween about 0.8 mm and 1 mm in diameter. Such diameters will allow thecatheter to be used as a guidewire for most conventional interventionalcatheters.

As the catheter of the present invention is to be used as a guidewire,it must be very flexible over its length, but also retain sufficienttorsional stiffness to allow rotation of the catheter to facilitatepositioning and guiding through the vascular system. Typically, thebending stiffness constant of the catheter will be below about 15in-lb-in, usually being from about 3 in-lb-in to 10 in-lb-in, andpreferably being from about 5 in-lb-in to 8 in-lb-in. The torsionalstiffness constant will be above about 0.5 in-lb-in/radian, usuallybeing from about 0.5 in-lb-in/radian to 5 in-lb-in/radian, andpreferably being from about 1 in-lb-in/radian to 3 in-lb-in/radian.Optionally, the flexibility of the catheter body may vary over itslength, with the higher flexibility (lower bending stiffness constant)being present near the distal end of the catheter.

As used herein and in the claims, bending stiffness constant (K_(B)) isdefined as

K_(B) =RFd,

where

R=bending radius (in.);

F=deflection force (lb.); and

d=length of catheter body section (in.)

The bending stiffness constant may be measured using a conventional3-point compression tester, such as the Instron Tensile CompressionTester. The catheter body section is placed on a pair of supports spacedapart by a known length (L). A deflection force (F_(d)) is applied tothe catheter body section at a location midway between the supports onthe resulting deflection measured. The bending radius (R) can then bedetermined from the measured deflection. Alternatively, the radius canbe determined by graphical analysis. In either case, the bendingstiffness constant (K_(B)) can then be calculated using the aboveformula.

As used herein and in the claims, torsional stiffness constant (KT) isdefined as:

K_(T) =τL/θ,

where

τ=applied torque on catheter body section (in-lb)

L=length of catheter body section (in); and

θ=angle of wind up over length (radians).

The torsional stiffness constant may be measured by attaching a knownlength (L) of the catheter body from one section at one end to agoniometer and at the other end to a torque measuring instrument. Thegoniometer is used to apply a known "wind up" (i.e., number of turnsmeasured in radians) to one end of the catheter body section while theresulting torque is measured at the other end. The torsional stiffnessconstant (K_(T)) may then be calculated using the above formula.

Such requirements of flexibility and torsional stiffness are best met bycoiled constructions, particularly by nested coil constructions havingtwo or more layered coils, which are coated with a polymeric material onthe outside, such as teflon, polyurethan, and the like. Conveniently,the catheter body may be formed using conventional techniques of thetype which are used for making movable guidewires. Such techniques arewell described in the patent and scientific literature. See, forexample, U.S. Pat. Nos. 4,747,406; 4,724,846; 4,682,607; and 3,416,531,the disclosures of which are incorporated herein by reference.

A housing is attached to the distal end of the catheter body. Thehousing will usually be a continuous shell or sheath which creates aninternal volume which is contiguous with the central lumen of thecatheter body. Preferably, the shell will be closed but may includeopenings for specific purposes. The housing both protects and providesmechanical support for the moving components of the ultrasonic imagingsystem, as described in more detail hereinbelow. Thus, the housingshould be formed from an acoustically transparent material to allow forultrasonic imaging therethrough. The housing will usually be rigid inorder to maintain a desired alignment of internal imaging components,but in some cases may possess a small degree of flexibility so long asthe operation of the imaging system is not substantially degraded. Thehousing will usually have a length in the range from about 1 cm to 2 cm,more usually from about 1.4 cm to 1.6 cm, and a diameter in the rangefrom about 0.3 mm to 1 mm, usually from about 0.8 mm to 1 mm.

A drive cable is provided within the central lumen of the catheter bodyand extends from beyond the proximal end to beyond the distal endthereof. The drive cable must also be axially flexible but torsionallyrigid since it must be able to both bend with the catheter body whilebeing able to deliver torque down its entire length to the imagingsystem, as described in greater detail hereinbelow. The diameter of thedrive cable will, however, be substantially less than that of thecatheter body, typically being from about 0.25 mm to 0.6 mm, moretypically being from about 0.5 mm to 0.6 mm. Methods for formingsuitable drive cables are described in U.S. Pat. No. 5,108,411, thedisclosure of which is incorporated herein by reference.

An ultrasonic imaging system is disposed within the housing and coupledto the drive cable in order to provide for rotation of at least some ofthe system components. The basic considerations in constructing animaging system suitable for use in the catheter of the present inventionare described in U.S. Pat. Nos. 4,794,931, and 5,000,185, thedisclosures of which are incorporated herein by reference. Theconstructions described in the U.S. patent and copending patentapplication may be modified as necessary to adapt the imaging system foruse in the much smaller housing of the present invention. The ultrasonictransducer will necessarily be much smaller, typically being shapedcylindrically with a diameter from about 0.3 mm to about 0.9 mm and alength in the range from about 1 mm to 1.6 mm.

Referring now to FIG. 1, a presently preferred embodiment of theguidewire imaging catheter of the present invention will be described.The guidewire imaging catheter 10 includes a catheter body 12 having adistal end 14 and a proximal end (not illustrated). A housing 16 issecured to the distal end 14 of the catheter body 12 and includes afixed guidewire 18 attached to its distal end. The fixed guidewire 18will normally include a deviated tip which is useful in guiding thecatheter through branches in the vascular system. The construction anduse of such deviated-tip fixed guidewires are amply described in themedical and patent literature.

The catheter body 12 includes a flexible wire coil 20 which is coatedwith a polymeric layer 22 composed of a suitable polymer, such asteflon, polyurethane, and the like. Other constructions of the catheterbody 12 within the parameters described above might also find use. Adrive cable 24 extends from the proximal end (not illustrated) of thecatheter body 12 to the distal end 14 and into housing 16. The drivecable 24 includes wires 26 which are connected to the ultrasonic imagingsystem, as described in more detail hereinbelow. The wires 26 serve tointerconnect an ultrasonic transducer of the imaging system with theexternal electronics (not illustrated) needed to both excite thetransducer and to interpret ultrasonic energy reflected back from theblood vessel wall.

An ultrasonic imaging system 30 within the housing 16 includes anultrasonic transducer 32 having a piezo-electric element 34 at itsdistal end. The transducer 34 and piezo-electric element 34 are alignedto project ultrasonic energy generally in the forward axial direction,where such energy will encounter a reflective surface 36. The reflectivesurface 36 is inclined at an angle of about 45° relative to the axialdirection so that the ultrasonic energy will be reflected radiallyoutward from the housing 16. It will be appreciated that by adjustingthe angle of surface 36, the projected energy can be directed forwardlyor rearwardly of the true radial direction.

The ultrasonic transducer 32 and reflective surface 36 are rigidlyattached to each other by a strut member 38. The proximal or rearwardend of the transducer 32 is mounted on the distal end of drive cable 24,and the distal end of drive cable 24 in turn is mounted within aproximal bearing 40 which is secured within a bearing retainer 42located generally at the distal end of housing 16. Similarly, the distalend of reflective surface 36 is mounted on a locking pin 44 which isreceived within a distal bearing 46. In this way, the rigid assembly ofthe transducer 32, reflective surface 36, and strut member 38, can berotated between the bearing members 40 and 46 by rotation of drive cable24. This is a preferred manner of construction because of the extendeddistance between the transducer 34 and the exterior of housing 16,providing for improved near field imaging capability. Additionally, themechanical joining of the mirror 36 to the transducer 34 improves theirmutual alignment and enhances the imaging capability.

Referring now to FIG. 2, an alternate construction of the guidewireimaging catheter of the present invention will be described. Thecatheter 50 includes a catheter body 52, a drive cable 54, and a housing56, each of which is generally the same as the corresponding componentdescribed with reference to FIG. 1. Catheter 50 further includes a fixedguidewire 58 and a pair of connecting wires 60 which may also beidentical to those earlier described. The imaging system 62 employed bythe catheter 50, however, differs from that earlier described in that noreflective surface is employed. Instead, a rotating transducer 64 isattached to rotate with drive cable 54 and includes a pair ofpiezo-electric elements 66 and 68. The first piezo-electric element 66is oriented at an angle of about 45° relative to the axial direction sothat it is able to project and receive ultrasonic energy directed in aforward conical pattern about the housing 56. The second piezo-electricelement 68 is oriented to project and receive ultrasonic energy in agenerally radial direction relative to the housing 56 so that an annularscan path may be achieved. The use of rotating ultrasonic transducers toprovide imaging is described in greater in U.S. Pat. Nos. 4,794,931, and5,108,411, the disclosures of which have previously been incorporatedherein by reference.

Referring now to FIG. 3, a second alternate embodiment of the imagingcatheter of the present invention will be described. The catheter 70includes catheter body 72, a drive cable 74, and a housing 76, each ofwhich may be the same or similar to the corresponding componentdescribed in connection with the embodiment of FIG. 1. The housing 76further includes a fixed guidewire 78 at its distal tip, and theconstruction of the guidewire may be the same as that previouslydescribed. An imaging system 80 within the housing 76 includes a fixedultrasonic transducer 82 located proximate the distal end of the housing76 and is oriented to project ultrasonic energy generally in theproximal or rearward axial direction. The transducer 82 is externallyconnected through a pair of wires 84 which are brought rearward throughthe catheter body 72. A reflective surface 86 is mounted at the distalend of the drive cable 74 and is inclined so that it is able to reflectthe ultrasonic energy in a generally radial direction as the reflectivesurface is rotated.

Referring now to FIGS. 4-7, the method of the present invention will bedescribed. In particular, a blood vessel BV, having a region of stenosisS is located within a branch thereof, will be imaged using the imagingguidewire 10 described above. Imaging guidewire 10 is introduced to theblood vessel BV by conventional techniques and brought to the regionproximate the branch under fluoroscopic control. As the branch isapproached (FIG. 4), the catheter 10 may be rotated until the fixedguidewire tip 18 enters the desired branch of the blood vessel havingthe stenosed region S.

After the guidewire tip 18 enters the branch, the catheter 10 is movedforward so that the housing 16 is able to enter the stenosed region S.The guidewire tip 18 will then extend beyond the stenosed region, whilethe catheter body 12 extends backward through the main branch of theblood vessel to the point of entry. The imaging system 30 within thehousing 16 may then be used to image the stenosed region by sweeping theultrasonic signal radially about the housing 16, typically at a rate inthe range from about 50 rpm to 2000 rpm, preferably from about 600 rpmto 1500 rpm. One or more cross-sectional images of the stenosed region Smay then be obtained by the methods described in U.S. Pat. Nos.4,794,931 and 5,000,185, the disclosures of which have previously beenincorporated herein by reference.

After the nature of the stenosed region S has been determined to thedesired extent, a method of therapeutic treatment can be selected. Forexample, it may be desirable to treat the stenosed region S with adilatation balloon catheter. In that case, a dilatation balloon catheter90 having a distal balloon 92 may be introduced over the imagingguidewire 10 in a generally conventional manner. The dilatation ballooncatheter 90 will include a central guidewire lumen having dimensionscompatible with the imaging guidewire 10 so that the balloon 92 may bebrought within the stenosed region S (FIG. 6). By then inflating thedilatation balloon 92, as illustrated in FIG. 7, the stenosed region Smay be compressed and blood flow through the blood vessel BV restored.After the balloon 92 is deflated, the catheter 90 may be moved backslightly to again expose the housing 16 so that the region S may againbe imaged. Based on such imaging, the need to further treat the bloodvessel can be assessed.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it will be obvious that certain changes and modificationsmay be practiced within the scope of the appended claims.

What is claimed is:
 1. An improved vascular imaging and interventionalmethod wherein a stenosed region in a blood vessel is treated with aninterventional catheter, said improvement comprising imaging thestenosed region using an imaging guidewire which is movably disposedwithin the interventional catheter, wherein the interventional catheteris used for treating the stenosed region.
 2. An improved method as inclaim 1, comprising extending an imaging system of the imaging guidewiredistally beyond the distal end of the interventional catheter in orderto image the stenosed region.
 3. An improved method as in claim 2,comprising positioning an imaging system of the imaging guidewire withinthe interventional catheter while the stenosis is being treated.
 4. Animproved method as in claim 1, comprising generating a generally axialultrasonic imaging signal and rotating a reflective surface within theimaging guidewire, where the reflective surface is disposed totransversely reflect the generally axial ultrasonic imaging signal.
 5. Amethod as in claim 4, wherein the reflective surface is rotated at arate in the range from about 50 rpm to 2000 rpm.
 6. A method as in claim1, comprising rotating an ultrasonic transducer within the imagingguidewire catheter, where the transducer is disposed to project anultrasonic imaging signal transversely relative to the catheter.
 7. Amethod as in claim 1, wherein the interventional catheter is initiallyintroduced over the imaging guidewire.
 8. A method for imaging andtreating a diseased region within a blood vessel, said method comprisingthe following steps:treating the diseased region with an interventionalcatheter; moving a drive cable relative to the interventional catheterto position an ultrasonic transducer at the diseased region, wherein thedrive cable is unconnected to the interventional catheter; and rotatingthe drive cable within the interventional catheter to scan the diseasedregion of the blood vessel with the ultrasonic transducer.
 9. A methodas in claim 8, wherein the drive cable and ultrasonic transducer arerotated within a guidewire positioned within the interventionalcatheter.
 10. A method as in claim 9, wherein the guidewire remainsstationary relative to the blood vessel while the interventionalcatheter is moved thereover.
 11. A method as in claim 9, wherein theinterventional catheter remains stationary relative to the blood vesselwhile the guidewire is moved therein.
 12. A method as in claim 8,wherein at least one treating step is performed prior to performing themoving step.
 13. A method as in claim 8, wherein the treating stepcomprises inflating a balloon on the interventional catheter to dilate astenosed region of the blood vessel.